(1) Field of the Invention
The present invention relates to a color picture tube device that is used in a television, a computer display or the like, and in particular to a technique for correcting YH misconvergence in the color picture tube device.
(2) Related Art
Generally in a color picture tube a magnet is provided at each of the top and bottom (hereinafter top/bottom magnets) at the front of a deflection yoke to correct upper and lower pincushion raster distortion (hereinafter simply referred to as xe2x80x9craster distortionxe2x80x9d). However, a side effect of correcting raster distortion with top/bottom magnets is the occurrence of YH misconvergence. FIG. 1 illustrates YH misconvergence.
In FIG. 1, an electron beam R (red) and an electron beam B (blue) should be irradiated in the center of the screen in a horizontal direction, but instead diverge in the horizontal direction the closer they become to the upper and lower edges of the screen in the vertical direction. The cause of this divergence in the horizontal direction is the vertical direction component of the electric fields generated by the top/bottom magnets.
Japanese patent number 2667215 discloses one example of a technique for correcting YH misconvergence in a color picture tube device. This color picture tube has four-pole coils on the electron gun side of the deflection yoke, and corrects YH misconvergence by supplying a vertical deflection current to a YH misconvergence correction circuit (hereinafter xe2x80x9cYH correction circuitxe2x80x9d) that includes the four-pole coils.
FIG. 2 shows the structure of the YH correction circuit. In FIG. 2, a YH correction circuit 140 is composed of a circuit that is composed of a four-pole coil 141 that is connected in serial to a circuit in which a diode 143 and a resistor 142 that are connected in parallel, and that is connected in parallel with a circuit having the same structure in which a diode 145 is connected in the opposite direction to the diode 143. The circuits are connected to a vertical deflection coil by a terminal 147.
However, while the amount that YH misconvergence is corrected (hereinafter xe2x80x9cYH correction amountxe2x80x9d) by the YH correction circuit 140 increases linearly in proportion to the size (absolute value) of vertical deflection current, the amount of YH misconvergence increases in a parabola shape the closer it becomes to the edge portions in the vertical direction.
For this reason, when misconvergence in the horizontal direction at the edge portions is resolved using the YH correction circuit 140, the YH correction amount is excessive in the area between each edge portion in the vertical direction and the center of the screen, causing residual misconvergence. FIG. 3 shows misconvergence (hereinafter xe2x80x9cYH windingxe2x80x9d) that remains after correcting YH misconvergence using the YH correction circuit 140. Here, R and B diverge in the area between either edge portion in the vertical direction and the center of the screen due to over-correction.
To solve this problem, Japanese laid open patent application number 4-298942 discloses a convergence correction device which combines diodes in multi-stages and varies the YH correction amount in accordance with the size of the vertical deflection current, to reduce YH winding. FIG. 4 shows the circuit structure of the disclosed convergence correction device. In FIG. 4, a resistor 153 is connected in series to a circuit in which a diode 152 and a resistor 155 are connected in parallel.
A circuit 151 composed of a plurality of diodes connected in series is connected to a circuit composed of the diode 152 and resistors 153 and 155 in parallel. Furthermore, a coil 154 is connected in series to the circuit. Another circuit that has the same structure as the circuit that includes the coil 154 and whose diodes are arranged in the opposite direction to those in the circuit 151 are connected in parallel to the circuit that includes the coil 154. Together these circuits compose a YH correction circuit 150.
In the YH correction coil 150, diodes connected in tandem switch to vary the amount of vertical deflection current, thus varying the amount of current that passes through the coil. Such a construction reduces residual YH winding by varying in stages the rate at which the YH correction amount increases, in response to increases in the amount of current.
However, in recent years rapid advances in color picture tubes have lead to flattening of panels and wider deflection angles, with a purpose of reducing the length of the picture tube. As a result, stronger top/bottom magnets are being used to correct raster distortion that has worsened compared to prior art. For these reasons YH misconvergence is becoming markedly worse.
Furthermore, for the same reasons, the high order components of YH misconvergence has increased and YH misconvergence bends to a much greater degree. Consequently, YH winding cannot be improved sufficiently using conventional techniques.
In order to solve the above-described problems, the object of the present invention is to provide a color picture tube device capable of accurately correcting YH misconvergence, even when YH misconvergence worsens markedly.
In order to achieve the aforementioned objective, the color picture tube of the present invention is a color picture tube composed of an electron gun that includes three inline cathodes, including: a set of YH misconvergence correction coils; and a set of coma aberration correction coils that generates a magnetic field to correct YH misconvergence, by different amounts of currents being supplied to each coil that composes the set of coma aberration correction coils, according to an amount of vertical deflection current.
According to the stated construction, YH misconvergence can be corrected accurately and residual YH winding that occurs after correcting YH misconvergence can be controlled, regardless of the degree of YH misconvergence.
In addition, the coma correction coil, which is a necessary compositional element of a color picture tube, is used in YH misconvergence correction. Therefore, YH misconvergence can be corrected with fewer components and a simpler circuit structure than conventional techniques, and without the addition of special components.
Furthermore, it is desirable that a pair of cores is provided, the cores being arranged on opposing sides of electron beams emitted from the electron gun, the YH misconvergence correction coils are respectively wound around the cores, the coma aberration correction coils are respectively wound around the cores, and vertical deflection current is diverted to the set of YH misconvergence correction coils and the set of coma aberration correction coils.
According to the stated construction, the coma correction coil and the four-pole coil share the cores. Therefore, the components in the color picture tube can be reduced in number and mounted with greater accuracy. An example of the cores is U-shaped cores, the U-shaped cores being positioned respectively above and below the electron beams in opposition to each other so that legs of one U-shaped core face legs of the other U-shaped core. A further example of the cores is E-shaped cores, the E-shaped cores being positioned respectively on left and right sides of the electron beams in opposition to each other so that legs of one E-shaped core face legs of the other E-shaped core.
Describing the present invention in terms of circuit structure, the present invention may be described as, as shown in FIG. 9, a color picture tube composed of an electron gun that includes three inline cathodes, including: an upper YH misconvergence correction coil; a lower YH misconvergence correction coil that is provided in opposition to the upper YH misconvergence correction coil with regard to electron beams emitted from the electron gun; an upper coma aberration correction coil that is provided on the same side as the upper YH misconvergence correction coil with regard to the electron beam; a lower coma aberration correction coil that is provided in a position that opposes the upper coma aberration correction coil with regard to the electron beams; a first switching element that is connected to a circuit so as to conduct when the electron beams scan an upper side of a screen; a second switching element that is connected to a circuit so as to conduct when the electron beams scan an lower side of the screen; a YH misconvergence correction circuit composed of (1) a first circuit in which a circuit composed of the lower YH misconvergence correction coil and the first switching element connected in series is connected in parallel to the upper coma aberration correction coil, and (2) a second circuit in which a circuit composed of the upper YH misconvergence correction coil and the second switching element are connected in series is connected in parallel to the lower coma aberration correction coil, the first circuit and the second circuit being connected in series, wherein vertical deflection current is diverted to the YH misconvergence correction circuit.
According to the stated construction, YH winding can be controlled and YH misconvergence can be corrected using a simple circuit structure, without having to provide a complicated circuit structure. Note that the first switching element and the second switching element may be diodes.
Furthermore, in terms of technical significance, the present invention is a color picture tube composed of an electron gun that includes three inline cathodes, including: a first circuit that has a four-pole magnetic field generated by diverting vertical deflection current to a pair of coils that are positioned in opposition to each other with regard to electron beams emitted by the electron gun; and a second circuit that has a four-pole magnetic field generated by diverting vertical deflection current to a pair of coils that are positioned in opposition to each other with regard to the electron beams, the four pole-magnetic field generated by the second circuit having the same polarity as the four-pole magnetic field generated by the first circuit.
According to the stated structure, the high order components of YH misconvergence can be dealt with while achieving a sufficient amount of correction.
Describing the technical significance in terms of circuit structure, the present invention is a color picture tube composed of an electron gun that that three inline cathodes, including: a first circuit that is composed of (1) a circuit in which a first coil and a first diode are connected in series connected in parallel to (2) a circuit in which a second coil that is positioned in opposition to the first coil with regard to electron beams emitted by an electron gun is connected in series to a second diode, the first diode and the second diode conducting in mutually opposite directions; a second circuit that is connected in series to the first circuit, and is composed of (3) a circuit in which a third coil and a third diode are connected in series connected in parallel to (4) a circuit in which a fourth coil that is positioned in opposition to the third coil with regard to the electron beams is connected in series to a fourth diode, the third diode and the fourth diode conducting in mutually opposite directions, wherein vertical deflection current is diverted to the first circuit and the second circuit.
In particular, taking the high order components of YH misconvergence into account, it is preferable that a circuit composed of a plurality of diodes that conduct in the same conduction direction as the first diode and that are connected in series is connected in parallel to the first diode, and a circuit composed of a plurality of diodes that conduct in the same conduction direction as the second diode and that are connected in series is connected in parallel to the second diode, the number of the plurality of diodes that conduct in the same direction as the second diode being equal to the number of the plurality of diodes that conduct in the same direction as the first diode. Furthermore, the present invention is a color picture tube composed of an electron gun that includes three inline cathodes, including: an upper coma aberration correction coil; a lower coma aberration correction coil that is positioned in opposition to the upper coma aberration correction coil with respect to electron beams emitted by the electron gun; a first switching element that is positioned so as to conduct when an upper side of a screen is being scanned; a second switching element that is positioned so as to conduct when a lower side of the screen is being scanned; and a YH misconvergence correction circuit composed of (1) a first circuit in which the first switching element and the upper coma aberration correction coil are connected in parallel, and (2) a second circuit in which the second switching element and the lower coma aberration correction coil are connected in parallel, the first circuit and the second circuit being connected in series, wherein vertical deflection current is diverted to the YH misconvergence correction circuit.
According to the stated construction, YH misconvergence can be corrected with use of the coma aberration correction circuit.
The present invention, based on the above-described technical ideas, is able to correct YH misconvergence accurately and at a low cost, even when YH misconvergence worsens markedly.